Pathology has several critical roles in studies of aging biomarkers. It can provide morphological correlates of functional changes that occur in aging and may suggest mechanisms for functional biomarkers. Data from a particular animal can be excluded from a data set if it has a purturbing randomly occurring lesion. Lesions can also be viewed as biomarkers in themselves. This is so for lesions that occur sporadically with increasing frequency as animals age and for those that progress in severity in most of all animals. This 5 year program is designed to study all tissues in 30 animals of each of the possible groups available from the Biomarker Program of the NIA: 2 species, 6 genetypes, 2 sexes, 2 diet groups, restricted and ad libitum fed, and a full range of 6 monthly time intervals from 6 to 30 months and older if possible. As many animals as possible will be studied by other investigators before necropsy. Data for each of the kinds of lesions occurring in the animals will be evaluated and the prevalence of each lesion will be compared between the various groups. Some lesions will be semiquantitatively evaluated for severity. Data will be studied for differences between species, genotypes and sexes and most importantly between age and diet groups. Correlations between functional biomarkers and lesions will be studied. The data generated will serve to classify, characterize and define the lesions occurring in the animals used in the Biomarker Program. The data will be useful for all investigators involved in the Biomarker Program.